Dc-stabilizer with preregulator



C- O. OLSSON DC STABILI ZER WITH PREREGULATOR June 3, 1969 Sheet Filed Jan. 13. 1967 United States Patent Int. Cl. H02m 1/08, 7/00 US. Cl. 321-18 2 Claims ABSTRACT OF THE DISCLOSURE Generally, the invention is directed to a DC. stabilizer having a preregulator including at least two electronic switching elements each of which "is series connected between the input and output terminals of the assemblage and in which each electronic element includes at least two electrodes so biased that a potential difference is developed therebetween, with such potential difference being different for the several elements, one of the electrodes for each element being connected to control means, and with the elements being controlled through the control means in such a manner that only one thereof is conductive at the time, that is to say, during the time interval when the input voltage is within the operative range of the respective elements.

The present invention refers generally to DC-stabilizers and especially to such stabilizers with preregulator.

DC-stabilizers with preregulators are previously known but are relatively expensive and complicated. One type includes an adjustable transformer with servo motor control, it may alternatively be hand controlled, but such a type is rather unusual. At present controlled rectifiers are most usual or one can make use of so-called switching, i.e. a pulse time modulation is created before a choke coil in order to obtain a variable DC-voltage for the preregulator.

The object of the preregulator is to prevent the series element in the stabilizer arrangement from being too power consuming and to keep the efficiency of the stabilizer at a reasonable level.

The arrangement according to the invention actuates the series" element or elements to perform a switching on the stabilized DC-side, thus obtaining a disconnection of those parts of the DC-voltage which are not needed. The series elements may be either tubes or transistors; it is only necessary to match the detail coupling of the stabilizer to the used element type. The disconnecting operation is made successively by excluding the series elements one by one as the voltage passes their respective voltage range.

The invention will be more closely described in connection with the accompanying drawings where:

FIG. 1 shows an arrangement according to the invention and including two series elements, and

FIG. 2 shows the invention with three series elements.

FIG. 1 shows the preferred embodiment of the invention, wherein the input of the system comprises a rectifier bridge including diodes Dl-D4, and one diagonal branch thereof is connected across the secondary winding L of a transformer. One of the other diagonal points of the bridge is connected to the anode of a tube V1, which acts as series element in the coupling and the second of these other diagonal points is connected to a base output terminal 0. A second series element V2 has an anode connected to a tap on the transformer winding L. The cathodes of the tubes V1 and V2 are interconnected at point p but held at different voltage levels by aid of a Zener diode Z in the cathode circuit of tube V1. Point p is connected to the second output terminal UT of the arrangement.

A reference voltage source RS is series connected to a 3,448,369 Patented June 3, 1969 potentiometer P1, P2 between the output terminals UT and O. A tap on the potentiometer is connected to an amplifier P, which in turn is connected to the interconnected grid electrodes of the tubes V1 and V2, The arrangement further includes necessary coupling condensers C1C3, preferably electrolythic condensers. The reference source RS and comparing resistance network P1 and P2, provide a regulation by which a deviation in output voltage from the desired value is constantly used to apply a bias control to the grids of V1 and V2 via the regulating amplifier F in such a way as to neutralize the deviation. The illustrated arrangement is for sake of simplicity shown with two series elements but it is understood that more than two easily can be included in the arrangement which thus can be adapted to actual need and use.

FIG. 1 shows the arrangement according to the invention with grid control. Cathode control is of course also possible and this is illustrated in connection with the embodiment in FIG. 2, which shows a typical power rectifier where .the bridge has the shape of a voltage doubling arrangement. The diodes D and the condensers C are here equalized with respect to voltage, which makes the illustrated winding arrangement possible with the input via the secondary windings L1-L3 between every second diode and capacitor respectively. Three series elements V1-V3 are here shown as tubes with their grids connected to resistors R1-R3 in order to make an adjustment to different voltage levels possible. These resistors are here shown as adjustable resistors connected to the reference RS, which in turn via a potentiometer coupling P1, P2 is connected to base potential, here represented by point 0. A tap on the potentiometer is connected to the amplifier F, which in turn via a transistor T is connected to the interconnected cathodes of tubes Vl-V3.

The connection of the series elements included in the arrangement is made by introducing a voltage difference between two electrodes, in the illustrated example between grid and cathode. This voltage difference has to be made different for the various series elements. If control on all cathodes is wanted and if plus is at the top of the figure the lowest voltage level is applied to the grid of the uppermost element V1 and successively higher voltage levels are then applied to the following grids in turn.

Starting with full input voltage the uppermost element only will be conducting at the beginning; all the other elements are blocked. Then the voltage decreases successively until current just starts to flow through next series element. At the first moment the tendency then will be that the potential difference between grid and cathode is relatively low as the potential of the grid was somewhat adjusted upwards from the beginning. This means a high current flow for which the regulating system automatically reacts by regulation on the cathode via amplifier F in such a way that the current is adjusted to a proper value and this in turn results in the disconnection of the upper element. The above described operation is then repeated and a disconnection of the series elements the one after the other can be obtained. Too high current results in an increase of the output voltage to nondesirable levels and this is sensed by the arrangement according to the invention, which reacts in accordance with the described regulation process.

The arrangement according to the invention makes a step-wise regulation possible (not a continuous) and thus also a more accurate regulation. It is however not suitable for use in connection with very expensive set of apparatus for high power values. The use will thus mainly be in connection with high power rectifiers for small power values where a splitting of the primary voltage is actual and in connection with smaller transistor regulators, where cheap switching is desirable.

Iclaim:

1. A DC-stabilizer with preregulator including at least two electronic switching elements each of which is series connected between input and output terminals of the stabilizer and where the input is applied viatransforrner windings in connection with a rectifier, characterized by each of said electronic series elements having at least two electrodes so biased that a potential difference is created therebetween, said potential difference being different for the various elements, the series elements being triodes, the anodes of which are connected to different points on said transformer winding, one of said electrodes in each triode being connected to a control device, the cathode electrodes of said triodes being biased to different potential levels by suitably selected and interconnected coupling elements; the triodes being controlled through said control device in such a way that only one of them is conducting at the time i.e. during the time interval when the input voltage is within the operative voltage range of the respective elements.

2. A DC-stabilizer with preregulator including at least two electronic switching elements each of which is series connected between input and output terminals of the stabilizer and where the input is applied via transformer windings in connection with a rectifier, characterized by each of said electronic series elements having a grid and at least two electrodes so'biased' that a potential differ- References Cited UNITED STATES PATENTS 2,590,180 3/1952 Juhola 321-18 2,985,813 5/1961 Garfinkel 321-48 3,083,328 3/1963 Mallery et a1. 321-16 3,358,209 12/1967 Kanngiesser 321--18 XR JOHN F. COUCH, Primary Examiner.

W. M. SHOOP, 1a., Assistant Examiner.

US. Cl. X.R. 323-22, 38, 39 

